Enzymatic saccharification of hydrogen peroxide-treated solids from hydrothermal processing of rice husks

Rice husks were subjected to hydrothermal processing in aqueous medium to cause the degradation of xylan to xylooligosaccharides. The resulting solid phase, with enhanced contents of cellulose and lignin, was assayed as a substrate for enzymatic hydrolysis either directly or after treatments with hydrogen peroxide in alkaline media under a variety of operational conditions. Solid yield, solid composition and susceptibility to enzymatic hydrolysis were assessed by empirical modelling. The susceptibility of the solids to enzymatic hydrolysis was greatly improved by peroxide treatments. Under selected conditions (oxidizing treatments with 50 g hydrogen peroxide/100 g solids at 80 °C for 4 h using a liquor to solid ratio of 15 g/g) lignin was removed in high proportion, and cellulose was almost quantitatively recovered in solid phase. In the subsequent enzymatic hydrolysis (using an enzyme/substrate ratio of 25 FPU/g at liquor to solid ratio of 15 g/g for 48 h), 67.9% of cellulose was converted into glucose, leading to a medium containing 43.5 g glucose/L. Higher cellulose conversions were achieved when the liquor to solid ratio employed in the enzymatic hydrolysis was increased, but then the final glucose concentrations decreased owing to the higher amount of liquid.